It is already known, in particular from European Patent Application EP-642 886 (Mitsuboshi), that a ribbed belt can have a backing layer, a cushion layer in which cords are disposed longitudinally, and a "compression" layer in which reinforcing fibers are embedded in a lateral direction of the belt, and on which the ribs of the belt are formed by machining a plane blank, generally by means of a grinding roller, which wastes a considerable amount of material, namely about 30%. Such machining of the ribs uncovers the ends of the reinforcing fibers so that they protrude from the outside of the ribs, and it also nicks the surface of the ribs, thereby forming tear start lines, in particular in the convex regions where the top of each rib meets its sides.
European Patent Application EP 0 633 408 proposes to apply a thin layer of rubber to the top of each of the ribs so as to coat the protruding fibers and to eliminate the tear start lines. This complicates manufacturing by adding another step.
The solution proposed in Application EP-642 886, which consists in not machining the tops of the ribs and in creating a concave recessed zone between the flat top of each rib and each of its sides, the recessed zone not making contact with the pulley, makes it possible to solve the problem only where it is at its worst, without remedying the problem of the tear start lines that machining can cause, or the problem of wastage of material.
In practice, the life of machined belts is generally shorter than that of other types of belt.
It is however desirable to have belts whose ribs have protruding fibers because such fibers tend to reduce the operating noise of the belt in certain applications.